Implementation of the dictionary in oC

I. Basic concepts of dictionaries

The dictionary (nsdictionary, nsmutabledictionary) in foundation is a data set composed of key-value pairs, just as we define words in the dictionary.

Key (key) is used to find the corresponding value. Key is usually a String object or any other type of object. in a dictionary object, the key value must be unique.

In addition, the key and value of the dictionary object cannot be null (nil). If you need to add a null value to the dictionary, you can add the nsnull object.

Ii. Immutable dictionary-nsdictionary

1: Initialize (with one element and multiple elements ):

// Initialize with a key-Value Object

Nsdictionary * DIC = [nsdictionary dictionarywithobject: @ "Lu can sample" forkey: @ "Lucan"]; nslog (@ "% @", DIC ); nslog (@ "% @", [DIC objectforkey: @ "Lucan"]); // output the number of DIC key-value pairs nslog (@ "% d", DIC. count); // create a key-Value Pair nsdictionary * dic1 = [nsdictionary dictionarywithobject: @ "Lu can lab 2" forkey: @ "sample"] using multiple methods; nslog (@ "% @", [dic1 objectforkey: @ "sample"]); nsdictionary * [email protected] {@ "first": @ "2301 ", @ "Sec": @ "2034"}; nsdictionary * dic3 = [nsdictionary dictionarywithobjectsandkeys: @ "Liu Xiang", @ "name", @ "sample", @ "name1 ", nil]; // output result nslog (@ "---- % @", dic2, dic3 ); // put vaule and key in an array into a variable array nsarray * [email protected] [@ 123, @ 668, @ 345]; nsarray * [email protected] [@ "first ", @ "swcond", @ "third"]; nsdictionary * dic4 = [nsdictionary dictionarywithobject: Values forkey: Key]; nslog (@ "xxxxxxxxxxxx % @", dic4 ); // sort nsarray * arry = [dic4 keyssortedbyvalueusingselector: @ selector (compare :)]; nslog (@ "++ % @", arry ); // use an existing dictionary object to initialize another new dictionary object (create a mutable object) nsdictionary * arry1 = [[nsdictionary alloc] initwithdictionary: dic4]; nslog (@ "ooooooo % @", arry1); // Save the object to the content file nsstring * Path = @ "/users/Apple/desktop/test. plist "; [dic2 writetofile: path atomically: Yes]; // read the dictionary object nsdictionary * Data = [nsdictionary dictionarywithcontentsoffile: path] from the previously saved file; nslog (@ "XXXXX % @", data); // dictionary traversal key1 is equivalent to I in a [I], and dic4 is the Dictionary defined by itself (ID key1 in dic4) {ID vaule = [dic4 objectforkey: key1]; nslog (@ "qqqqqq % @", key, vaule);} //-(void) removeobjectforkey :( ID) akey; // delete key-value pairs nsmutabledictionary * dic7 = [nsmutabledictionary dictionarywithdictionary: dic2]; [dic7 removeobjectforkey: @ "Sec"]; nslog (@ "% @", dic7 ); // Add [dic7 setobject: @ "3412" forkey: @ "Sec"]; nslog (@ "% @", dic7) If no key value is replaced ); // Add a dic4 dictionary without sequence [dic7 addentriesfromdictionary: dic4]; nslog (@ "% @", dic7 );